Coded Light (CL) is visible light that carries embedded information which is encoded in a form such that the presence of the additional information is imperceptible by the human visual system. Generally, this means that the encoding is based on the use of high-frequent modulations of the light intensity. The encoded information can be anything, from a lamp-specific identifier to an HD-TV signal. The disclosed invention is primarily focused, but not limited to, the use of CL for the identification of different light sources, as well as the identification and quantification of their separate light contributions, or footprints, in the illuminated scene. The detection of lamp-specific identifiers facilitates localization during commissioning of large lighting systems, but also enables localized light control of the detected lamps. Additionally, the lamp specific identifiers can form a basis for location-based services such as indoor navigation, or for the localized transmission of maintenance information.
As CL light involves high-frequency light modulations, it is commonly detected using photodiodes. These, however, only provide point measurements, which is cumbersome in the presence of multiple Coded Light sources and does not provide information about the spatial footprint, i.e. the geometric intensity distribution and spatial localization of light contribution from each individual light source in a scene.
It has been previously demonstrated that Coded Light can also be detected using conventional global shutter cameras by employing exposure times that are sufficiently short to detect a single code bit in every frame. By accurately tuning frame rate and code characteristics, the entire code is then read sequentially over multiple frames. This approach, however, results in very slow read-out capacity and suffers from low light sensitivity.